The present invention relates to a contacting caliper gauge and more particularly to a contacting caliper gauge suitable for measuring the thickness of thin sheet material.
Caliper gauges are well known in sensor technology. In general, they are used for a variety of purposes, viz measuring the thickness of sheet material. They have been of two types, i.e., contacting and non-contacting. A typical non-contacting caliper gauge, having air bearings, is disclosed in U.S. Pat. No. 3,528,002. Although non-contacting gauges are in theory suitable for all applications and are superior to contacting ones (superior in the sense of not having the gauge possibly contaminate the sheet through contact), in certain applications contacting gauges must be employed. For example, in the paper industry, because there is a certain amount of compressibility in the paper, a measurement of the paper by a contacting gauge would differ from a measurement of the paper by a non-contacting gauge. The United States paper manufacturers have formed an association (TAPPI) to promote uniform standards for the paper industry. The TAPPI standard is that measurement of thickness must be based upon results obtained from a contacting gauge at a certain pressure level. A typical contacting gauge is disclosed in U.S. Pat. No. 3,828,248. However, heretofore all contacting caliper gauges have suffered from the shortcoming that for very thin sheet material, such as tissue, the gauge has a tendency to tear the sheet.